As one piece of information transmitted with a communication system or information recorded in an accumulation device, there is an image or a moving image. In the related art, technologies for coding images are known to transmit and accumulate such images (hereafter including moving images).
As a moving image coding scheme, AVC (H.264/MPEG-4 Advanced Video Coding) and High-Efficiency Video Coding (HEVC), which is a succession codec, are known (NPL 1).
In such a moving image coding scheme, normally, a predicted image is generated based on a local decoded image obtained by coding/decoding an input image, and a predicted residual (also referred to as a “difference image” or a “residual image” in some cases) obtained by subtracting the predicted image from an input image (original image) is coded. An inter-screen prediction (inter-prediction) and in-screen prediction (intra-prediction) are exemplified as a method of generating a predicted image.
In intra-prediction, predicted images are sequentially generated in a picture based on a local decoded image in the same picture.
In inter-prediction, a predicted image is generated through inter-picture motion compensation. In most cases, information regarding motion compensation (motion compensation parameter) is not directly coded to reduce a coding amount. Accordingly, in inter-prediction, the motion compensation parameter based on a decoding situation or the like in the periphery of a target block is estimated.
In recent years, hierarchy coding technologies for hierarchically encoding images according to necessary data rates have been proposed. As one of the representative hierarchical coding schemes, Scalable HEVC (SHVC) is known (NPL 2).
In SHVC, spatial scalability, temporal scalability, and SNR scalability are supported. For example, in the case of the spatial scalability, an image subjected to down-sampling to a desired resolution from an original image is coded as a lower layer. Next, in a higher layer, inter-layer prediction is performed in order to remove inter-layer redundancy.
As inter-layer prediction, there is inter-layer motion information prediction in which information regarding motion prediction is predicted from information regarding of a lower layer of the same time and inter-layer image prediction (inter-layer texture prediction) in which a predicted image is generated from a decoded image of a lower layer of the same time.
In SHVC, any one of inter-prediction, intra-prediction, and the inter-layer image prediction can be used to generate a predicted image.
In inter-layer image prediction of SHVC, a decoding target picture and a decoded image of the lower layer of the same time are used. Therefore, the decoded image of the lower layer is retained in a buffer for reference.